What is titanium dioxide?
Inert earth mineral used as a thickening, whitening, lubricating, and sunscreen ingredient in cosmetics. It protects skin from UVA and UVB radiation and is considered to have no risk of skin irritation (Source: Skin Therapy Letter, 1997, volume 2, number 5). Because of its gentleness, titanium dioxide is an excellent sunscreen active for use on sensitive or rosacea-affected skin. It is also great for use around the eyes, as it is highly unlikely to cause stinging in this area.
Although titanium dioxide is a natural ingredient, pure titanium dioxide in nature is almost always adulterated with potentially harmful contaminants such as lead and iron. Therefore, titanium dioxide is purified via synthetic processes for use in cosmetics and sunscreens.
Titanium dioxide is typically micronized and coated for use in cosmetic products. The micronizing makes this somewhat heavy-feeling ingredient easier to spread on skin, not to mention making it more cosmetically elegant. Micronized titanium dioxide is also has much greater stability and can provide better sun protection than non-micronized titanium dioxide. Micronized titanium dioxide does not penetrate skin so there is no need to be concerned about it getting into your body (well, unless you eat the stuff). Even when titanium dioxide nanoparticles are used, the coatings employed have a larger molecular size that keeps the nanoparticles of titanium dioxide from penetrating beyond the uppermost layers of skin. This means you're getting the ample sun protection titanium dioxide provides without any risk of it causing harm to skin cells.
The coating process is done to improve application, enhance sun protection, and also to prevent titanium dioxide from interacting with other ingredients in the presence of sunlight, thus enhancing its stability. It not only makes this ingredient much more pleasant to use for sunscreen, but it improves efficacy and eliminates safety concerns. Common examples of ingredients used to coat titanium dioxide are alumina, dimethicone, glycerin, silica, and trimethoxy capryl silane.
Titanium dioxide as used in sunscreens also undergoes surface modification to ensure efficacy and stability. Examples of surface modifier ingredients used for titanium dioxide include stearic acid, isostearic acid, polyhydroxystearic acid, and dimethicone/methicone copolymer.
Titanium dioxide in mineral sunscreen
Some Web sites and doctors maintain that titanium dioxide is inferior to zinc oxide, another mineral sunscreen whose core characteristics are similar to titanium dioxide. We’re not sure where the information about titanium dioxide not being a great active sunscreen ingredient came from but the reality is titanium dioxide is a great broad-spectrum SPF ingredient and is widely used in all manner of sun protection products the world over.
What gets confusing for some consumers is trying to decipher research that ranks sunscreen ingredients by a UV spectrum graph. By most standards, broad-spectrum coverage for any sunscreen ingredient is defined as one that surpasses 360 nanometers (abbreviated as “nm”, this is how the sun’s energy is measured). Titanium dioxide surpasses this measurement, but depending on whose research you look at, it either performs as well as or slightly below zinc oxide.
Although it's true that titanium dioxide does not rank as high for UVA protection as zinc oxide, it ends up being a small measurement of difference (think about it like being 10 years old versus 10 years and 3 months old). This is not easily understood in terms of other factors affecting how sunscreen actives performs (such as the base formula) so many, including some dermatologists, assume that zinc oxide is superior to titanium dioxide for UVA protection. When carefully formulated, titanium dioxide provides excellent UVA protection. Its peak UVA protection is lower than that of zinc oxide, but both continue to provide protection throughout the UVA range for the same amount of time.
Additional sources: The Encyclopedia of Ultraviolet Filters, Allured Publishing, Nadim A. Shaath, PhD, 2007, pages 16-19; Skin Pharmacology and Applied Skin Physiology, Volume 14, Supplement 1, 2001, pages 92–97; Toxicology In Vitro, Volume 20, Issue 3, April 2006, pages 301–307; Toxicology Science, Volume 115, Issue 1, May 2010, pages 156–166.